Continuous-Operation Modular Rotating Fusion Engine

Continuous-Operation Modular Rotating Fusion Engine Iván Moreno Gil September 18, 2025 Abstract This invention describes a Continuous-Operation Rotating Modular Fusion Engine–Reactor based on a rotating and modular architecture, composed of a plurality of independent polyhedral fusion cells (preferably hexagonal pyramids) arranged radially around a central rotor. Each cell integrates deuterium–tritium fuel pellet injection systems, ignition modules (lasers or equivalent drivers), and diagnostic/control ports located at the structural vertices. The flat base of each cell functions as a hot plate, coupled to a shared neutron energy harvesting and conversion blanket (Neutron Energy Harvester, NEH) manufactured with advanced materials (W–SiC, RAFM), and further supported by an integrated IGBI radiator plate that enhances lateral heat spreading, improves Brayton efficiency, and reduces thermomechanical stress. The rotation of the rotor imposes a cyclic sequence: injection →ignition →energy release →cooling, distributed in parallel across the dozens of cells per rotor and, at plant scale, across thousands of cells coordinated in multi-rotor campuses. This configuration ensures continuous electricity production, in contrast to the discrete discharges of inertial confinement, and offers a modular and scalable pathway compared to the monolithic chambers of tokamaks. The design incorporates staged thermal management, replaceable hot-plate cartridges, the integrated IGBI radiator, and optional magnetohydrodynamic (MHD) conversion, ensuring high efficiency, simplified maintenance, and fault tolerance. Technical Field The invention belongs to the field of nuclear fusion reactors, with specific application to modular rotating architectures for continuous operation. Its primary objective is the steady generation of electrical power with high power density and rapid industrial scalability, although the same technology can also be extended to long-range space propulsion systems. 1 Contents 1 Background of the Invention 4 1.1 Motivation and Safety Justification .............................. 5 2 Summary of the Invention 6 3 Claims 7 4 Detailed Description of the Invention 10 4.1 Hexagonal Pyramid Fusion Cell (Individual Module) .................... 10 4.1.1 Energy Balance per Cell and Calibration ....................... 14 4.1.2 Cell Durability and Maintenance ........................... 16 4.2 Rotor Energy Balance ..................................... 17 4.3 Rotor “tick” architecture (12 stations, 2 ignition points) ................... 20 4.4 Operating Cycle and Performance (architecture with NEH dome) ............. 21 4.5 NEH Blanket and Integration ................................. 23 4.6 Detailed Architecture of the NEH Dome: Truncated Hexagonal Prism (Specifications) . . 24 4.6.1 Macroscopic geometry ................................. 24 4.6.2 Ports and “sniper-holes” ................................ 24 4.6.3 Layer stack ....................................... 26 4.6.4 IGBI system (Gas–Brush Impingement Interface) .................. 26 4.6.5 Thermal budget and limits ............................... 26 4.6.6 Integrated module (MIDH / BEM) .......................... 26 4.6.7 Functional summary .................................. 27 4.7 Risks and mitigations: thermo–mechanical fatigue, coupling alignment, and vibration control .............................................. 27 4.8 Design of the Staged Cooling System ............................. 30 4.8.1 IGBI interface (pressurized He jets + TZM pin–fins) ................ 30 4.8.2 Sectorized gaseous pre–cooling ............................. 30 4.8.3 Service and maintenance window ........................... 30 4.8.4 Clearance control and integration ........................... 30 4.8.5 Note on thermo–mechanical clearance. ........................ 31 4.8.6 Energy balance per shot ................................ 31 4.8.7 Properties of candidate materials ........................... 31 4.8.8 Margin with respect to structural materials ...................... 31 4.8.9 Scalability ........................................ 31 4.8.10 Note on rotary joints .................................. 32 4.9 Architecture of the Neutron Energy Harvester (NEH) and material specifications ..... 33 4.9.1 Functional stack (plasma face →interior) ...................... 33 4.9.2 Thermo–mechanical properties (guideline ranges) .................. 34 4.9.3 Neutronic parameters and TBR ............................ 34 4.9.4 Hydraulic and thermal sizing (baseline FLiBe) .................... 35 4.9.5 Chemical management and tritium extraction .................... 35 4.9.6 Fabrication, QA/QC and maintenance ........................ 36 4.9.7 Limits and lifetime ................................... 36 4.9.8 Performance closure (baseline without MHD in chain) ................ 36 4.10 Maintenance and Cartridge Replacement ........................... 36 4.11 Laser and Sensor Assembly (Apex + Edge Pods) ...................... 38 2 4.12 Unit Cost and Mass per Cell (bottom–up model, RAFM structure + W–SiC PFC + FLiBe) 40 4.13 Cost per rotor and per campus ................................ 41 5 Economic Feasibility Study 43 5.1 Methodology and assumptions ................................. 43 5.2 CapEx per rotor and LCOE (example: 24-cell rotor) .................... 43 5.3 Margins at π= 75 €/MWh .................................. 44 5.4 Modular deployment and ramp–up .............................. 44 5.5 Executive summary ....................................... 45 5.6 Impact of material and process improvements ........................ 45 5.7 Consolidated economic comparison (MRFEP vs. fission) .................. 45 6 Real comparison: Fission nuclear plant vs. MRFEP plant 47 6.1 Reference case: Almaraz Nuclear Power Plant (Spain) .................... 47 6.2 Scenario A: Energy equivalence with a 1.2 GW nuclear plant ................ 47 6.3 Scenario B: Equivalence in land use (100 ha footprint) ................... 48 6.4 Direct comparison ........................................ 48 6.5 Sensitivity notes ......................................... 48 7 Future Work and Roadmap 49 A Complementary and optional technologies 50 A.1 Magnetohydrodynamic (MHD) conversion .......................... 50 A.2 Direct conversion of radiation and particles .......................... 50 A.3 Advanced materials and hybrid breeders ........................... 51 A.4 Other future optimization routes ............................... 51 B Example of a Full-Scale MRFEP Plant Implementation 52 B.1 Site layout and land requirements ............................... 52 B.2 Reactor Building (RB): geometry and shielding ....................... 52 B.3 Underground reactor hall and shielded basements ...................... 53 B.4 Power conversion and auxiliaries ................................ 53 B.5 Personnel and Operations ................................... 53 B.6 Surface area and staffing comparison ............................. 53 B.7 Energy scenarios and household equivalents ......................... 54 3 1 Background of the Invention Conventional fusion systems include: •Tokamaks and stellarators: large toroidal chambers based on continuous magnetic confinement, requiring intense fields (B∼5–10 T), complex cryogenic systems, and structures on the order of tens of meters. Although they have demonstrated sustained plasma confinement for several seconds, they suffer from MHD instabilities, disruptions, and high maintenance costs. See “ITER Physics Basis” [1], Pedersen et al. [2], and Federici et al. [3]. •Inertial confinement fusion (ICF): spherical targets compressed by high-energy lasers in nanosecond pulses, as in the NIF or OMEGA facilities. They have achieved scientific gain (Qfus >1) in single-shot demonstrations, but repetition at high cadence (>1Hz) remains unsolved in practice due to optical damage, pellet logistics, and driver energy costs. See Le Pape et al. [4], Hurricane et al. [5], and Meyerhofer et al. [6]. •Multi-chamber or sequential ignition proposals: such as Dubrovsky (2023) and Woodruff (2010), which proposed distributing ignition across multiple targets or secondary chambers. While conceptually mitigating localized loads, they have not proposed industrializable architectures nor solutions for continuous heat and neutron management, see Dubrovsky [7] and Woodruff [8]. These approaches face recurring limitations: 1. Concentrated neutron loading: highly localized fluxes rapidly degrade first walls (∼MW/m2), requiring frequent replacements, see Federici et al. [3] and Zinkle and Ghoniem [9]. 2. Restricted duty cycles: both superconducting magnets and laser systems suffer from thermal and radiation fatigue, reducing availability to scales of days or weeks. See Devred et al. [10] and Zinkle and Ghoniem [9]. 3. Lack of continuous operation: none of the current systems achieve a stable baseload regime comparable to fission or combined cycles. See Stacey [11] and Agency [12]. There is therefore a need for an architecture that: •Distributes neutron and thermal loads spatially and temporally. •Simplifies driver requirements by distributing ignition across multiple smaller chambers. •Enables industrial modularity: progressive scaling from tens of MW to GW without fundamental redesign. •Provides intrinsic fault tolerance, eliminating the risk of catastrophic interruption from a single-cell failure. •Operates in continuous mode, making its commercial use viable as a clean energy producer. 4 1.1 Motivation and Safety Justification The main motivation of this invention lies in the broad safety margin offered by modular fusion architectures compared to fission reactors and monolithic confinement systems. See Dean [13] and Maisonnier et al. [14]. Key differences include: •Absence of sustained chain reaction. Each cell requires an external driver pulse and a fuel pellet; without them, fusion ceases instantly. No runaway conditions exist. •Minimal fuel inventory. Active fuel is limited to milligrams of D–T per ignition. Even at full-plant scale, the circulating quantity corresponds only to grams, compared to tons of fissile uranium or plutonium in conventional reactors. See International Atomic Energy Agency [15]. •No residual decay heat. In a shutdown (driver SCRAM or seismic trigger), all thermal generation halts within microseconds. Unlike fission, there is no residual power that threatens overheating, see Zohuri [16]. •Seismic and impact resilience. In the event of earthquakes or external impacts, the maximum consequence is shielding damage and possible release of small traces of tritium or activated structural material. There is no possibility of a Chernobylor Fukushima-type accident. For more information, see Cadwallader [17] and Federici et al. [18]. •Engineered confinement. The reactor is housed in reinforced concrete vaults with 1.5–2 m biological shields. Robotic handling and modular cartridges minimize exposure during maintenance. This safety profile enables siting plants closer to consumption centers, reduces emergency planning zones, and differentiates the Modular Rotating Fusion Engine (MRFE) substantially from fission plants and monolithic fusion facilities. 5 2 Summary of the Invention The invention proposes a Modular Rotating Fusion Engine (MRFE) whose novelty resides in the geometry and mechanics of the system rather than in speculative or undeveloped technologies. The concept is structured around: 1. A rotor integrating multiple polyhedral fusion cells (we use as example hexagonal pyramids) arranged radially, each acting as a repetitive micro-fusion chamber. 2. Each cell undergoes an autonomous cycle: pellet injection →laser ignition →energy absorption in the NEH blanket →staged cooling, with characteristic cooling times τcool ∼5s, enabling continuous reuse. 3. A shared Neutron Energy Harvester (NEH) blanket within each cell, composed of functional layers (plasma-facing, moderator, breeder/coolant, structural shielding) to absorb neutron flux, breed tritium, and extract usable heat. 4. Dual energy conversion: (i) via Brayton/sCO2thermodynamic cycles for recovered heat, and (ii) optionally via MHD channels at cell edges, directly converting a fraction of charged-particle energy into electricity. 5. A rotating configuration in which hot faces sequentially couple to fixed radiator/heat-exchanger stations, thereby avoiding thermal shocks and distributing loads evenly. Thermal coupling is realized through an integrated IGBI radiator plate (Impinging Gas Bearing Interface), combining helium microjets with high-conductivity pin–fin surfaces for efficient lateral heat spreading. 6. Modular scalability: from 24 up to 120 cells per rotor or more; rotors can be stacked axially or operated in parallel to assemble multi-GW plants. Progressive commissioning allows electricity generation to begin with the very first rotor. 7. Fault tolerance: a defective or failed cell reduces total output by less than 2% in a 60-cell rotor, maintaining continuous operation without systemic risk. In summary, the MRFE provides an alternative to traditional fusion approaches by leveraging existing industrially mature technologies: high-energy Nd:glass lasers, see Campbell and Glenzer [19] and al. [20]; first-wall materials such as RAFM steels and W–SiC composites, see Zinkle and Busby [21] and al. [22]; Brayton/sCO2thermodynamic cycles, see al. [23]; advanced metallic additive manufacturing (WAAM, SPF/DB), see Martina et al. [24] and al. [25]; and robotized remote-handling systems, see Taylor and Davis [26]. The true innovation lies in the rotating modular architecture and the integrated IGBI radiator plate, not in the development of the base technologies. 6 3 Claims 1. (Rotating architecture and continuous regime) A rotating fusion reactor comprising a rotor with multiple independent polyhedral fusion cells, configured to receive fuel and ignition pulses, wherein the cells sequentially rotate through injection, ignition, energy extraction, and cooling, maintaining a continuous energy production regime. 2. (Preferred cell geometry) The reactor of claim 1, wherein the cells are hexagonal pyramids with their bases acting as hot faces aligned with fixed radiator/heat exchanger stations. 3. (Alternative geometries) The reactor of claim 1, wherein the cells are alternatively pentagonal pyramids, triangular pyramids, or other convex polyhedra providing flat hot faces compatible with stationary thermal coupling. 4. (Multilayer NEH blanket) The reactor of any of the preceding claims, comprising a Neutron Energy Harvester (NEH) multilayer blanket including: (i) a plasma-facing component in W or W– SiC, (ii) an intermediate moderator, (iii) breeder/coolant channels with LiPb or FLiBe, and (iv) a structural shield in reduced-activation ferritic–martensitic (RAFM) steels or functional equivalents. 5. (NEH dome coupled to hot face) The reactor of any of the preceding claims, comprising an NEH dome coupled to the hot face of each cell, configured as a prism or truncated pyramid congruent with the cell geometry, integrating functional layers, sniper-holes, coolant manifolds, and mechanical/electrical couplings in a replaceable cartridge, see Fig. 5. 6. (Ignition drivers) The reactor of any of the preceding claims, wherein ignition drivers (lasers, ion beams, or equivalents) are mounted at the apex and/or edges of the cells, delivering synchronized pulses with a delay of less than 10 ps. 7. (Cell-per-rotor scale) The reactor of claim 1, wherein the rotor couples to a central bus and accommodates between 24 and 120 cells or more per rotor, with possible concentric rings and/or axial stacking, enabled by the intrinsic modularity of the architecture. 8. (Interchangeable modular cartridge) The reactor of any of the preceding claims, comprising amodular interchangeable cartridge on the hot face of each cell, removable and insertable by robotic means during continuous operation. 9. (Frictionless thermal interface) The reactor of any of the preceding claims, comprising a thermal interface system between the hot face and the stationary radiator, based on capillary liquid films, isothermal coupling, or pressurized helium jet systems (IGBI radiator interface), or other frictionless interfaces designed to transfer heat with minimal wear. 10. (Direct conversion) The reactor of any of the preceding claims, wherein optionally metallic liquid coolant channels (LiPb, doped FLiBe, or conductive equivalents) are installed to act as magnetohydrodynamic (MHD) ducts for direct electrical energy conversion (see Appendix A). 11. (Rotor thermal-gradient mitigation) The reactor of any of the preceding claims, further comprising a rotor thermal-gradient mitigation system configured to maintain the temperature of the bearing ring within a predetermined margin and reduce differential expansion relative to the cells; wherein the preferred embodiment is an isothermal IGBI radiator ring with internal cooling channels, and alternatively flexible cooled interfaces or equivalent variants may be used to achieve the same function. 7 12. (Cell-level fault tolerance) The reactor of any of the preceding claims, wherein the functional independence of each cell provides fault tolerance, such that isolated ignition failures or off-nominal events cause only proportional power reductions without compromising overall rotor operation. 13. (Optics and sensor protection) The reactor of any of the preceding claims, wherein optics and sensors are protected by replaceable shields and barriers, including sacrificial windows and ceramic shutters, robotically interchangeable. 14. (Low-activation structural materials) The reactor of any of the preceding claims, wherein back plates and support structures are fabricated in RAFM steel or other low-activation equivalents, improving thermal conductivity, radiation resistance, and cost. 15. (Additive manufacturing and lightweighting) The reactor of any of the preceding claims, wherein cells and modular cartridges are manufactured by metal additive manufacturing technologies (WAAM, L-PBF, SPF/DB), incorporating topological lightweighting and lattices of equivalent stiffness to reduce mass and unit cost. 16. (Staged cooling) The reactor of any of the preceding claims, further comprising a staged cooling system, wherein hot faces are sequentially coupled with fixed radiators at the external station, distributing the thermal load of the cycle evenly. 17. (Plant scalability) The reactor of any of the preceding claims, wherein the modularity of cells and rotors allows configurations ranging from a single rotor (tens of MW) to multi-rotor campuses (hundreds of MW up to several GW), with progressive commissioning from the first installed rotor. 8 Correspondence with detailed description. Each of the above claims is supported by the technical sections of the document: •Claim 1 →Sections 4.1 and 4.3 •Claim 2 →Section 4.1 •Claim 3 →Section 4.1 •Claim 4 →Sections 4.4 and 4.8 (multilayer NEH blanket) •Claim 5 →Section 4.5 (detailed NEH dome architecture) •Claim 6 →Section 5.4 (ignition drivers and synchronization) •Claim 7 →Section 4.2 (scaling to 120 cells per rotor) •Claim 8 →Section 5.5 (interchangeable modular cartridges) •Claim 9 →Sections 5.1 and 4.6 (capillary/frictionless thermal interface, IGBI) •Claim 10 →Section 5.3 (MHD liquid-metal coolant channels) •Claim 11 →Section 4.2 (isothermal IGBI ring and thermal management) •Claim 12 →Section 4.4 (fault tolerance of independent cells) •Claim 13 →Section 5.4 (optics and sensors protected by barriers) 9 4.1.2 Cell Durability and Maintenance Objective. To ensure that each cell can operate in repetitive regime with minimal interruption, defining quantitative criteria for preventive replacement and robotic substitution procedures. Typical replacement sequence (robotized). 1. Hydraulic isolation and He purge of the NEH cartridge. 2. Removal of auxiliary power and mechanical lock of the anchor. 3. Disconnection of hydraulic dry-breaks (auto-sealing) and docking electrical connector. 4. Automated unscrewing of anchors by torque-controlled robots. 5. Extraction using telescopic dolly and transfer to maintenance/storage cell. 6. Insertion of new cartridge and verification of flatness, leak-tightness (He leak-test <10−9mbar·L/s) and realignment. Target times. •Robotized cartridge swap time: <15 min (design with 2 redundant robots). •Inline rapid inspection (thermography + UT): <5min per cartridge. •Optical window/shutter hot-swap:≤2min. Replacement frequency criteria. Cartridge lifetime is defined as the minimum among the following limits, applying a safety factor SF ≃0.7: •Thermo–mechanical fatigue (backplate, RAFM). Coffin–Manson–Basquin model with ∆T∼ 150–200 K per shot, α≈12 ×10−6/K, E∼200 GPa. Typical lifetime: Nf∼105–3×105cycles. ⇒replacement every 1–3 years at f= 0.25 Hz (1 shot/4 s). •Irradiation (DPA). Thresholds: W (5–10 dpa), RAFM (10–20 dpa). For flux ϕn∼1018 n/m2s on the first wall: DPA/year ∼5−10, tDPA ∼1−3 years. •Erosion/corrosion. Sputtering in W: ∆x∼0.01 mm/year. Corrosion in FLiBe: 0.05–0.1 mm/year (uncoated); <0.01 mm/year with SiC/Al2O3coatings. Estimated lifetime >20 years ⇒not governing. •Optics and sensors (ports). Transmittance decays as T(n)=T0e−βn, n0.9≈0.1053 β, with β∼10−6–10−5/shot. Typical lifetime 104–105shots. With multiplexing m= 3−4and f= 0.25 Hz ⇒T∼7–19 days. Hot-swap in 2 min ⇒downtime <0.03%. 16 Limit Key variable Model Typical lifetime Governing? Thermo–mechanical fatigue (RAFM) ∆T, f Coffin–Manson 1–3 years Yes Irradiation (DPA) Fluence, dpa/year Threshold 10–20 dpa 1–3 years Yes W erosion (PFC) Y, ΦRate mm/year 20–40 years No FLiBe corrosion mm/year Mitigated by SiC 20–50 years No Optics/windows (with m)β, f, m T(n)and T=Nm f 7–19 days (ex.: f=0.25 Hz, m=3−4) downtime <0.03% No Table 2: Estimated lifetime criteria for the NEH+dome+hot-plate cartridge and its ports. f(Hz) m N (shots) T(days) tswap (min) downtime 0.25 2 5×1044.63 2 0.030% 0.25 3 5×1046.94 2 0.020% 0.25 4 5×1049.26 2 0.015% 0.25 4 1×10518.52 2 0.0075% Table 3: Sensitivity of replacement interval T=Nm fand downtime ≈tswap/T. Synthesis. •The dominant lifetime limits are thermo–mechanical fatigue and irradiation, imposing cartridge replacement every 1–3 years. •Corrosion/erosion is not governing for horizons <10 years if protective coatings are applied. •Optics/windows require frequent replacement, but with multiplexing and hot-swap the impact on availability is negligible. Recommended frequency. •NEH+hot-plate cartridge: replacement every 1–3 years at f= 0.25 Hz; annual NDE inspection. •Complete module (dome+NEH+hot-plate): major replacement every 5–7 years. Integration note. The detailed description of dome NEH geometry, layers, and architecture is developed in Sec. 4.6. Complete cartridge swap and maintenance procedures are further expanded in Sec. 4.10, covering the cell level and the integrated replacement system. 4.2 Rotor Energy Balance Objective. To calibrate the net power and energy of a rotor from the net power per cell, and to set the Minimum Viable Product (MVP) as the minimum number of cells that yields a positive economic surplus (after amortization and OpEx), together with a Functional Reference Rotor (FRE) serving as a replicable design point. 17 Reference parameters per cell. Baseline scenario (Sec. 4.1): performance per cell Pe,cell =2.03 MW, Yfus = 20 MJ, fcell = 0.25 Hz, εcap ≈0.90, ξ ≈0.90, ηel ≈0.50. Operational availability u= 95% and average selling price π=75.9/MWh. Power and energy per rotor with Ncells. Pe,rotor(N)=N Pe,cell,(12) Eyear(N)=Pe,rotor ×8760 h ×u. (13) Annual revenues: Revenue(N) = Eyear(N)×π. MVP criterion (economic, conservative). We define MVP as the minimum Nsuch that the annual net surplus per rotor is positive: Surplus(N) = Revenue(N)−NCapExcell/Tamort | {z } annual amortization −NOpExcell | {z } operation and maintenance −OpExcommon >0, with conservative assumptions (no MHD, FLiBe, RAFM/W–SiC, WAAM/HIP): CapExcell ∈[4.0,5.0] M, Tamort = 10 years,OpExcell ≈0.15 M/year,OpExcommon ≈0.5 M/year. With Pe,cell = 2.03 MW and π= 75.9/MWh, the revenue per cell is: Revenuecell = 2.03 ×8760 ×0.95 ×75.9≈1.28 M/year. Amortization + OpEx per cell ≈(0.40−0.50)+0.15 = 0.55−0.65 M/year, hence the margin per cell is ∼0.63−0.73 M/year. Thus, the condition of positive surplus is met comfortably starting from N=18 (see table). Config. Cells N Pe,rotor [MW] Eyear (95%) [GWh] Revenue (95%) [M€/year] MVP (min. surplus >0) 18 36.54 304.1 23.08 FRE (functional reference) 24 48.72 405.4 30.77 32 cells 32 64.96 540.6 41.01 48 cells 48 97.44 810.9 61.52 60 cells 60 121.8 1,014. 76.89 Table 4: Rotor power, annual energy (with u= 95%) and revenue at π= 75.9/MWh for different N. Technical–economic reading. •With the baseline Pe,cell = 2.03 MW, the economic MVP is reached at 18 cells, leaving a margin above amortization+OpEx under conservative assumptions. •The reference rotor (FRE) with N= 24 cells delivers ∼48.7 MW net and ∼405 GWh/year, with revenues of ∼30.8 M/year. 18 •Scaling Nis linear in both power and revenues; the optimal decision will be made against available CapEx, operational risk, and plant ramp-up strategies (Sec. 5). Figure 2: Extended central rotor with 12 coupled fusion cells. The modular architecture —both of the rotor and the cells— allows the design to be extended to include additional layers of cells, enabling a wide variety of configurations. Modularity is only limited by the diameter and length of the central rotor, admitting more or fewer cells and ring-layers accordingly. 19 4.3 Rotor “tick” architecture (12 stations, 2 ignition points) Each rotor revolution is discretized into 12 stations with fixed dwell time per station tdwell =0.67 s (control with admissible variance up to 1.0s under contingency), and 2 diametrically opposed ignition stations. The kinematic magnitudes are defined as: Trev =Nest tdwell = 12 ×0.67=8.04 s,rpm =60 Trev =7.46 rpm. The per-cell cadence is fcell =Nign Nest tdwell =2 12 ×0.67 =0.25 Hz (1 shot every 4 s per cell). Note: fcell depends only on (Nest, Nign, tdwell)and is independent of the total number of rotor cells; the number of cells scales the total power, not the cadence of each cell. Station map (functional example). # Station Main function 1 Ignition A Firing + faceted shutter closure 2 IGBI–1 Hot discharge (impinging He + TZM pin-fins) 3 IGBI–2 Hot discharge (second stage) 4 Pre–He–1 Pressurized helium convection (polishing 1) 5 QA–1 Thermography, fluxmeters, pose verification 6 Service Service window: purges, micro-adjustments, optical hot-swap if required 7 Ignition B Diametral firing 8 IGBI–3 Hot discharge (third stage) 9 IGBI–4 Hot discharge (fourth stage) 10 Pre–He–2 Pressurized helium convection (polishing 2) 11 QA–2 Secondary inspection and validation 12 Buffer/Bypass Operational margin (latency, synchronization, brief contingencies) Integration with the thermal cycle. The four IGBI stages (Stations 2,3,8,9) manage the pulse in a staggered manner, limiting ∆T/∆tat the hot-plate and keeping useful flux under the design threshold qmax; the pre-cooling stages (Stations 4 and 10) stabilize the wall at ∼600–800 K prior to QA/Service. Kinematic summary (baseline by ticks) Nest = 12, Nign = 2, tdwell = 0.67 s, Trev = 8.04 s,rpm = 7.46, fcell = 0.25 Hz. The step–and–dwell control accepts temporal variance per station up to 1.0 s under contingency, with automatic replanning to preserve the mean value of fcell. 20 4.4 Operating Cycle and Performance (architecture with NEH dome) Each fusion cell follows a repetitive cycle of fuel loading →ignition →energy collection →staged cooling →reload. The rotating assembly and temporal staggering between cells ensure that the rotor delivers essentially continuous power. Reference assumptions per cell •Geometry: hexagonal pyramid (s≈1.0m, Ahot ≈2.60 m2) with NEH dome coupled to the base. •Cryogenic D–T target; fusion energy per shot Efus =20 MJ. •Capture/conversion: εcap ≈0.90, transfer efficiency to cycle ξ≈0.90, and thermal-to-electric efficiency ηel ≈0.50 (Brayton sCO2with recuperator). No MHD in the baseline (see Appendix A for options). •Thermal interface at station: IGBI (pressurized He impinging jets + high-conductivity pin– fins/“forest”) in a controlled gap (∼0.5–1.0 mm), with heff ∼6,000–9,000 W m−2K−1. •Cadence: fcell =0.25 Hz (one ignition/4 s); cell availability u= 95%. •Net power per cell (calibrated): Pnet cell ≈2.03 MW. Validated baseline (per cell) Yfus = 20 MJ, fcell = 0.25 Hz, εcap = 0.90, ξ = 0.90, ηel = 0.50 ⇒Pe,cell ≈Yfus fcell (εcapξηel) = 20 ·0.25 ·0.405 ≈2.03 MW. (i) Fuel loading. •D–T pellets (sub-mg to mg) stored cryogenically. •Axial injection with alignment <50 µm and velocity 100–200 m/s (see Sec. ??). •Pre-optical verification and phase synchronization (jitter <10 ps). (ii) Ignition. •Drivers: cluster of Nd:glass lasers (351 nm) with redundancy and thermal load sharing. •Pulse: coupled energy ELto achieve nominal Efus = 20 MJ. •Species: ∼80% neutrons at 14.1 MeV, ∼20% αparticles at 3.5 MeV. (iii) Energy collection and pathways. •Interception dome+plate: the NEH dome and multilayer base absorb εcap ≈0.90 of Efus. •Thermal conversion: FLiBe in dome/backplate →recuperative heat exchanger →Brayton sCO2 cycle with ηel ≈0.50 (baseline without MHD). •Tritium breeding: 6Li(n,α)T in FLiBe (regeneration fraction ∼20%, see Sec. ??). •Shielding: the dome attenuates flux toward the apex, extending optics and sensor lifetime. 21 (iv) Staged cooling and step-and-dwell.The cycle scheduler defines 6 temporal slots per shot (total 4.0 s), with exact dwell tdwell =0.667 sper slot. Control admits extension up to 1.0s under contingency (e.g., thermal stabilization). The physical stator stations are ≥9(injection/ignition, 3–4 thermal IGBI, 2 deep cooling, inspection/QA, maintenance 1 and 2); not all are visited in every shot. 1. S0: injection+ignition (aligned with apex port). 2. S1–S3: thermal extraction IGBI (He jets 6–9 bar + pin–fins,heff ∼6–9 kW/m2K). 3. S4: deep cooling / recuperator (wall → ∼ 600–700 K). 4. S5: service window (quick inspection, QA); maintenance stations scheduled on demand. (v) Net energy per shot (consistency check). Eshot,el =Pnet cell fcell =2.03 0.25 ≈8.1 MJ,20 MJ ×0.90 ×0.90 ×0.50 ≈8.1 MJ. Table 5: Net production with NEH dome and IGBI interface (baseline Pnet cell ≈2.03 MW). Configuration N(cells) Pnet rotor [MW] Eyear (95%) [GWh] Notes FRE (24 cells) 24 48.7 405 Functional reference Medium scale 40 81.2 676 Higher modularity High platform 60 121.8 1,014 Full plant (vi) Rotor operation scenarios (baseline without MHD). (vii) Fault tolerance and lifetime. •Ignition failure: loss <4.2% (FRE, 24 cells); in 60 cells, ∼1.7%. •NEH+hot-plate cartridge: replacement every 1–3 years (∼105cycles); NEH dome longer lifetime (5–7 years). •Multiplexing and optical hot–swap minimize downtime (<0.05%). 22 4.5 NEH Blanket and Integration The pyramidal walls (103) surrounding the fusion cavity form a multilayer Neutron Energy Harvesting (NEH) blanket. Each layer is designed to sequentially absorb, moderate, and convert the 14 MeV neutron flux, while breeding tritium, extracting high-temperature heat, and providing structural integrity. Reference stack (baseline). 1. Plasma-facing layer (20–25 mm): sintered W–SiC tiles. Functions: •Resistance to thermal shocks >107W/m2. •Capture of αparticles (3.5 MeV, ∼20% of Efus). •Primary shielding against X-rays and charged particles. 2. Moderator/multiplier (30–40 mm): Be/BeO blocks interleaved with SiC. Functions: •Moderation of neutron spectrum from 14 MeV to 0.1–1 MeV (optimal for 6Li capture). •Neutron flux multiplication via (n,2n) reactions in 9Be. •Thermal diffusion and gradient buffering. 3. Breeder/coolant (60–80 mm): liquid FLiBe (6LiF–BeF2). Functions: •Tritium breeding via 6Li(n,α)T (σ∼940 barns). •Heat extraction at 700–800◦C for sCO2Brayton cycle. •Compatibility with SiC coatings to minimize corrosion/erosion. •Optional B4C laminates (2–3 mm) to capture residual neutrons. 4. Structural/back plate (20–30 mm): RAFM ferritic–martensitic steel (e.g., EUROFER97). Functions: •Mechanical support of the modular cartridge. •Integration of cooling microchannels and manifolds for extraction to exchangers. Thermal conversion path (baseline). Captured heat is conducted to a closed Brayton cycle with supercritical CO2, with efficiency ηel ∼0.45–0.50 under nominal operation. This value is adopted as the reference efficiency for rotor sizing. Advanced option (Appendix A). In alternative configurations with eutectic LiPb (17Li–83Pb), breeder channels may also function as MHD conduits under a dedicated B∼5T field. This would enable direct electrical conversion with additional efficiency ηMHD ∼5–10%, albeit at the cost of greater technological complexity. Modular shielding and replacement. The hot plate coupled to the NEH radiator is implemented as a removable cartridge, total thickness tplate ∼20–30 cm: •Robotized replacement every ∼105cycles (≈1.5years at nominal cadence). •Independent dome vs. plate replacement, reducing costs and downtime. •Modular architecture: local erosion or point activation does not compromise the entire cell. 23 4.6 Detailed Architecture of the NEH Dome: Truncated Hexagonal Prism (Specifications) This subsection develops the construction aspects of the NEH Dome and its integration into a removable integrated module (MIDH: Dome + Hot-plate + NEH). While Sec. 4.1.2 establishes lifetime and replacement criteria at the cell level, here the physical and engineering characteristics of the cartridge are detailed: geometry, layer stack, mechanical, hydraulic and electrical interfaces, as well as thermal budget and mass estimates. Throughout the document the following nomenclature is used: •NEH blanket: the global neutron energy extraction and conversion system of the plant. •Lateral NEH cartridge: removable modular unit on rails, including breeder+moderator+internal structures (1–2 year replacement). •Integrated Dome–HotPlate–NEH Module (MIDH): also termed Modular Removable Base (BEM), grouping the dome, hot-plate and full NEH (5–7 year replacement). 4.6.1 Macroscopic geometry •Type: truncated hexagonal prism (hexagonal base, six inclined faces, upper truncation). •Base side: s= 1.00 m, base area Ahot =3√3 2s2≈2.60 m2. •Internal height: Hdome = 0.22m(range 0.18–0.25 m). •Upper truncation: coaxial hexagon stop = 0.25mwith central axial port. •Back plate (dorsal): tdorsal = 20 mm RAFM/ODS (15–25 mm). 4.6.2 Ports and “sniper-holes” Central axial port (injection/diagnostics): •Internal diameter: ⊘100 mm (industrial standard criterion). •W liner 6 mm; faceted shutter with diaphragm-type opening (<5ms). •Coaxial axis tolerance <100 µm. Peripheral ports (auxiliary optics): •Number: 6 (one per face), inclination 12◦–18◦. •Diameter: ⊘40–50 mm, W liner 3–5 mm. •Labyrinth slot + local He purge. 24 Figure 3: Technical schematic of the truncated prism NEH Dome, showing geometry and nominal dimensions: base side s= 1.0m, height H= 0.25 m, central axial port ⊘100 mm with fast-closing faceted shutter (<5ms), and six peripheral ports ⊘40–50 mm (inclination 12–18◦), equipped with tungsten liners (3–5 mm). The design ensures compatibility with coaxial and peripheral laser beams while minimizing radiative leakage during operation. 25 4.8.10 Note on rotary joints The design avoids high-temperature liquid-metal rotary joints: FLiBe circulates in the fixed stator. The cartridge transfers energy only via the IGBI interface or co–rotating pad, simplifying logistics and increasing reliability. 32 4.9 Architecture of the Neutron Energy Harvester (NEH) and material specifications The multilayer NEH blanket constitutes the primary interface for capture and conversion of fusion energy (14.1 MeV neutrons and 3.5 MeV αparticles). Its design optimizes: (i) resistance to repetitive pulsed loading, (ii) neutron moderation/absorption down to the 6Li capture window, (iii) tritium breeding with TBR ≥1.05, and (iv) heat extraction at high flux density, integrated in the cell cartridge (Dome + hot-plate + NEH) described in Sec. 4.1 and Sec. 4.6. Scope and geometric variants. •Wall/blanket (pyramidal faces): thin stack, distributed load. •Base (hot-plate) with dome: reinforced first wall and larger hydraulic section, increasing capture fraction εcap by geometric flow bias. 4.9.1 Functional stack (plasma face →interior) 1. PFC (Plasma-Facing Component): W or W–SiC cermet. Wall:t=20–30 mm; Base:t=40–50 mm. Functions: stop α(∼20% Efus), withstand thermal shock, first nspectral conditioning. 2. Moderator/multiplier: Be/BeO and/or C/SiC, t=40–60 mm. Functions: slow down 14 MeV n →0.1–1 MeV; multiplication (n, 2n)in Be. 3. Breeder + coolant: baseline FLiBe (Li2BeF4) enriched in 6Li, t=60–80 mm, channels ∅20– 30 mm. Option: LiPb (17Li–83Pb) (see Appendix ??). 4. Absorber/fine shield: B4C / Gd2O3/ Hf, t=20–30 mm. 5. Rear structural plate: RAFM or Ti–6Al–4V, t≃20 mm, with microchannels and cartridge anchors. 33 4.9.2 Thermo–mechanical properties (guideline ranges) Table 6: Properties by layer/material (indicative in situ design values). Material T[K] k[W/mK] cp[kJ/kgK] ρ[g/cm3] CTE [10−6/K] Guideline limit W (PFC) 800–1200 120–170 0.13–0.16 19.3 4.5–5.0 ∆Tpulse ≤ 300 K; σeq <0.6σy W–SiC (PFC) 800–1200 60–110 0.20–0.35 11–15 5–6 Toughness ↑, thermal shock ↑ Be / BeO (mod.) 600–900 180–220 1.6–1.9 1.85 / 3.0 11–12 Encapsulated due to toxicity C/SiC (mod.) 700–1100 120–180 0.75–0.9 2.9–3.2 4–5 Low CTE; good diffusivity LiPb (breeder) 900–1100 12–16 0.20–0.30 9.4–10.5 25–30 Conductor; MHD option (App. A.1) FLiBe (breeder) 900–1050 1–2 1.9–2.2 1.9–2.1 20–22 Electrically insulating; chemically stable B4C (absor.) 600–900 15–30 0.75–0.85 2.5–2.6 4–5 10B: high thermal σa Gd2O3(absor.) 600–900 6–10 0.35–0.45 7.4 8–9 Gd-157: very high thermal σa Hf (absor.) 600–900 20–23 0.15–0.20 13.3 5–6 Ductile absorber in plates RAFM (plate) 600–800 15–25 0.45–0.60 7.7–7.9 11–12 Low activation; weldability Ti–6Al–4V (plate) 500–800 6–7 0.55–0.70 4.43 8–9 σy(500◦C) ∼450– 600 MPa 4.9.3 Neutronic parameters and TBR •Initial conditioning in PFC (W/W–SiC): γattenuation and controlled sputtering. •Moderation/multiplication: Be/BeO reduces Ento 0.1–1 MeV (6Li window) and multiplies flux via (n,2n). •Breeder: baseline FLiBe with enriched 6Li sized for TBR ≥1.05 at real angular coverage; LiPb option (App. A.1) when volumetric power density is prioritized. •Absorber: B4C / Gd2O3captures residual thermal tails and protects the rear plate. Neutron streaming through ports. The presence of sniper–holes and diagnostic/driver ports constitutes a potential leakage path for 14.1 MeV neutrons. Such streaming may (i) reduce the overall tritium breeding ratio (TBR) and (ii) activate structural components assumed to remain cold (e.g. rotor hub, optics). While the present baseline assumes TBR ≥1.05, this value is subject to confirmation. Dedicated Monte Carlo neutronic simulations (MCNP, Serpent) explicitly modeling port geometries and shutters will be required to quantify the impact of streaming and to validate breeding margins. Layered ceramic shutters and 6Li–enriched FLiBe are foreseen as mitigation strategies. 34 4.9.4 Hydraulic and thermal sizing (baseline FLiBe) Energy closure per cartridge (consistent with Secs. 4.4 and 4.2). Yfus = 20 MJ, fcell = 0.25 Hz, εcap = 0.90, ξ = 0.90, ηel = 0.50. Thermal power per cycle per cartridge: Pth,in =Yfus fcell (εcap ξ) = 20 ×0.25 ×0.81 ≈4.05 MWth. Net electric power (without MHD in the main chain): Pe,cell =Pth,in ηel ≈4.05 ×0.50 ≈2.03 MW. Required FLiBe flow. Taking ∆TFLiBe = 150 K (e.g. 950 →1100 K) and cp≃2.0 kJ/(kg K): ˙mFLiBe =Pth,in cp∆T≈4.05 ×106 2000 ×150 ≈13.5kg/s. Design guideline:˙m= 12−18 kg/sper cartridge (valve-adjustable) with typical channel velocities u= 1−3 m/s. Channel geometry and velocities. For circular channels ∅20−30 mm, the total hydraulic area required for u∼2.0 m/sis: Q=˙m ρ≈13.5 2000 ≈6.8×10−3m3/s, Atot =Q u≈3.4×10−3m2. With 36 channels of ∅20 mm (unit area ≈3.14 ×10−4m2), Atot ≈1.13 ×10−2m2⇒u≈0.6 m/s (very conservative regime). It is recommended to modulate the number of channels (24–60) to keep u∈[1,3] m/sand Re ∼104−105(turbulent). Dimensionless numbers (FLiBe, 1000 K). Re = ρuDh µ,Pr = µcp k(∼10−15),Pe = Re Pr. For Dh=25 mm, u=2 m/s, µ≈6×10−3Pa s, ρ≈2000 kg/m3:Re ≈1.7×104(turbulent). With k=1.5 W/mK,Pr ≈8−12. Use turbulent correlations with high Pr and short-entry thermal effects (dome blocks). LiPb option (quick reference; details in App. ??). With cp∼0.2 kJ/(kg K) and ∆T∼200 K, the same Pth,in requires ˙mLiPb ∼100 kg/s. Recommended u= 3−5 m/s, redox control, and ceramic coatings in the channel. 4.9.5 Chemical management and tritium extraction •FLiBe (baseline): redox potential control (Be/BeF2pairs), T extraction via He bubbling and cold traps; compatibility with ceramic insulators and metallic C-seals. •LiPb (option): Al/Zr getters, degassing, membrane permeators for T2/HT; protective coatings (selective aluminization, nitrides) at interfaces. •TBR: 6Li enrichment and full angular dome coverage guarantee TBR ≥1.05 at nominal cartridge power. 35 4.9.6 Fabrication, QA/QC and maintenance •Segmented PFC: W/W–SiC facets (brazing or diffusion), RT/UT on joints. •Microchannel blocks: L-PBF or HIP+machining; internal coating SiC/Al2O3. •Back plate (RAFM/Ti): forging+LAM, stress relief; INVAR inserts for CTE grading. •In-service NDT: phased-array UT, eddy currents; DTS fiber optics in channels. •Modules: BEM (Dome+NEH+hot-plate) and SC-NEH (lateral sub-cartridge) as per Sec. 4.6. 4.9.7 Limits and lifetime •PFC thermal shock: ∆Tpulse ≲300 K; gradient <5–8 K/mm. •Equivalent stresses: σeq <0.6σy(T); Miner Pni/Ni<0.2per cartridge. •Neutron fluence: replacement before 10–20 dpa in PFC/moderator (1–3 year window depending on cadence). •Corrosion/erosion: u≤5 m/son walls; redox control + coatings at high-shear corners. 4.9.8 Performance closure (baseline without MHD in chain) Yfus = 20 MJ, fcell = 0.25 Hz, εcap = 0.90, ξ = 0.90 ⇒Pth,in ≈4.05 MWth, ηel = 0.50 ⇒Pe,cell ≈2.03 MW. Note: the integration of MHD conversion with LiPb, its figures of merit (Ha, N,Rm) and partial electrical gains are documented separately in Appendix A.1 and are not part of the baseline energy chain in this section. 4.10 Maintenance and Cartridge Replacement Preliminary note. The physical architecture of the cartridges (dome+NEH+hot plate) is developed in Sec. 4.6, while their energy role per cell is analyzed in Sec. 4.1.1. Here we address exclusively the logic of maintenance and replacement at the system scale. Hot-plate cartridge design. Each fusion cell base integrates a modular NEH cartridge of 200– 300 mm, with typical stratification: •Front tile (20–30 mm): W–SiC, exposed to direct flux, designed to withstand thermal shocks ∆T∼200–300 K and 105cycles. •Intermediate slab (150–200 mm): breeder/coolant (FLiBe enriched in 6Li), with channels ⊘20– 30 mm for ˙m= 50–100 kg/s. •Back plate (30–50 mm): RAFM steel, with microchannels for secondary evacuation and shielding. Mounted on a three-point kinematic mount, with radial locking pins and prismatic guides ensuring positional repeatability of ±0.2mm even after dozens of replacements. 36 Robotic replacement system. The rotor operates in a tick-discretized regime (Sec. 4.3), such that a cell periodically aligns with fixed service stations: 1. Station Nx(extraction): a robotic arm releases the pins, disconnects services (fluid, sensors), removes the degraded cartridge, and places it into a shielded container with heavy/borated water for cooling. 2. Station Nx+1 (insertion): a second arm positions a new cartridge, aligns it with laser fiducials, and secures it with automatic pins. Sealing is validated with force sensors and 3D vision. Cycle time: 45–60 s per cartridge, compatible with continuous operation. Manipulator candidates. Industrial precedents demonstrate feasibility: •Fanuc M-2000iA/2300: payload 2.3 t, reach 3.7 m, repeatability ±0.2 mm. •KUKA KR QUANTEC ultra: payload 300 kg, repeatability ±0.06 mm (applicable to optical cartridges). •AREVA/Westinghouse telemanipulators: designed for fuel rods in fission reactors. •ITER Remote Handling System: replacement of FW modules of 4–6 t in irradiated environments. Replacement interval. For loads ∼1MW/m2and life Ncycles ∼105: tlife =Ncycles fcell =105 0.25 ≈1.1×106s≈4.6days. A replacement is scheduled every 3–5 days per cartridge. A staggered plan ensures that ∼2–3 cartridges are replaced per day in steady operation, without net power loss. Continuous operation and passive safety. •The rotor halts in intervals of 0.67 s, advancing in fixed ticks; each cell, during those 0.67 seconds, is in a different state of the cycle and performs its function within that time frame. •Degraded cartridges are sealed in borated steel containers for transport/reprocessing. •Redundant manipulators ensure continuity in the event of failure. •Global power impact: instantaneous drop <2% and full recovery within ∼1 min. Management of optical consumables and sensors. Windows, filters, and optical cartridges are integrated as interchangeable consumables using the same manipulators. With a lifetime of ∼104shots per window (∼11 h at 0.25 Hz), replacement is practically daily. The cost will depend on unit price; the development of coatings (Si3N4, DLC) is being considered to extend service life to 3–5 days, reducing logistics and operating expense. Operational balance. The modular replacement system maintains: ηavail >0.98 (global plant availability), ensuring continuity of electrical output and reducing inventory of critical parts. The strategy turns maintenance into a programmed and continuous operation, more akin to replacing printer cartridges than to major outage cycles of a conventional reactor. 37 4.11 Laser and Sensor Assembly (Apex + Edge Pods) Port placement strategy. To minimize neutron flux and direct thermal load, no ports are placed on the base or at its vertices. The final architecture combines: •Apex port (primary coaxial beam): traverses the symmetry axis of the truncated hexagonal pyramid, delivering the main beam to the target through internal folding optics. •Edge pods (auxiliary oblique beams): three or four pods embedded in the upper edges of the pyramid, at ∼2/3height relative to the base, each with an obliquity of 15–25◦toward the target. Laser cluster and redundancy. Each port mounts a triple cluster of high-energy lasers, operating in round–robin mode to distribute fluence, with hot–standby redundancy in case of failure. •Tripled Nd:glass (351 nm): NIF/LMJ reference; pulse energy 0.3–0.7 MJ. •KrF excimer (248 nm): high repetition, applicable to auxiliary pods. •OPCPA petawatt: ultrashort startup/conditioning pulses. The energy delivered per port is 0.3–0.7 MJ; with 4–5 active ports the total energy on target is 1–2 MJ. Deformable mirrors maintain phase error <10 ps and overlap <0.5mm on the pellet. Optical protection and consumables. Each port incorporates: •Sacrificial windows: baseline lifetime 104shots. •Segmented faceted windows (8–16 sectors): increase effective lifetime by ×8–12, reducing OPEX from ∼70 M€/year (unmitigated) to ∼1M€/year for a 24-cell FRE rotor. •Faceted ceramic shutters: closing ≤2ms during the harvest phase, distributing erosion. •Local dry He purges: prevent condensate deposition and extend optical lifetime. Replacements are performed hot using the same robotic manipulators as for the cartridges (Sec. 4.10), homogenizing maintenance logistics. Integrated sensorics. •Coaxial interferometry: through the axial port, measuring implosion and symmetry. •Fast photodiodes and scintillators: in edge pods, behind Be/SiC shielding, for timing and neutron spectrum. •Fiber-optic telemetry: data + clock distributed to the central bus; closed-loop pointing correction (<1mrad). 38 •Without segmentation: cost >70 M€/year in optical consumables (windows, filters) for a 24-cell FRE. •With coatings + segmentation (×105effective shots/window): cost ∼7–14 M€/year. •With 12-sector segmented window + He purge: cost ∼0.6–1.2 M€/year, level compatible with reference OPEX. This architecture makes maintenance economically viable, eliminating optics as a bottleneck. Parameter Nominal Range No. of ports 1 apex + 3 pods 1 apex + 4 pods Incidence (pods) 20◦15–25◦ Energy/port 0.5 MJ 0.3–0.7 MJ Total target energy 1.5 MJ 1–2 MJ Temporal phase error <10 ps <20 ps Pellet overlap <0.5mm <1.0mm Window lifetime (unmitigated) 104shots 5×103–2×104 Effective lifetime (segmented) 1.0–1.2×106depends on msectors FRE windows OPEX (24 cells) 0.6–1.2M€/year (with mitigation) Shutter time ≤2ms ≤5ms Table 7: Optical and sensor parameters (apex port + edge pods). Figure 5: Schematic cross-section of a fusion cell (truncated hexagonal pyramid with NEH dome). The coaxial beam from the apex and the auxiliary oblique beams from edge pods are represented. All converge on the D–T pellet, distributing energy and reducing localized damage on a single port. 39 4.12 Unit Cost and Mass per Cell (bottom–up model, RAFM structure + W–SiC PFC + FLiBe) Objective and scope. Bottom–up estimation of unit cost and mass for a hexagonal pyramidal cell in nominal configuration: RAFM steel structure (low activation), W–SiC PFC on hot–plate with dome, FLiBe breeder enriched in 6Li, and RAFM back plate. This configuration materializes the minimum-cost MVP, while maintaining adequate thermal and mechanical performance. Key processes (RAFM structure). •Lamination + CNC machining: RAFM panels 12–25 mm; drilling/manifolds; flange surfacing. •EBW/GTAW welding in inert chamber: panel joints, ribs, and supports; controlled preheating. •Modular assembly: ribs and stiffeners, docking flanges, cartridge seats, and positioning keys. •QA/QC: phased-array UT, eddy current testing, and leak testing (He <10−9mbar·L/s) in feedthroughs and flanges. Geometric assumptions (NEH with dome). Consistent with Secs. 4.9 and 4.8: hot base area Ahot ≈2.6 m2; W–SiC PFC tPFC = 45 mm; FLiBe breeder tbr = 120 mm (base with dome); RAFM back plate tback =30 mm; external pyramidal structure in RAFM (12–20 mm panels + ribs). Masses (nominal). Densities: ρWSiC ≈12,500 kg/m3,ρFLiBe ≈2,000 kg/m3,ρRAFM ≈7,800 kg/m3. mPFC =Ahot tPFC ρWSiC = 2.6×0.045 ×12,500 ≈1,463 kg, mbr =Ahot tbr ρFLiBe = 2.6×0.12 ×2,000 ≈624 kg, mback =Ahot tback ρRAFM = 2.6×0.03 ×7,800 ≈608 kg, mstruct ≈RAFM (walls+ribs) ⇒3.0–3.6t. Note: The higher Young’s modulus of RAFM (∼200 GPa) allows slightly thinner panels than Ti while maintaining flexural stiffness; the lower thermal conductivity of Ti compared to RAFM (6–7 vs 15–25 W/mK) makes RAFM preferable for lateral thermal spreading of the base. Raw material costs (bulk procurement). Guide prices: RAFM ∼7EUR/kg, effective W–SiC ∼110 EUR/kg, FLiBe enriched (base with dome) equivalent cost ∼0.30–0.60 M EUR/cell (includes 6Li surcharge and nuclear-grade fuel salt). Cmat(RAFM struct)≈(3.3t)×7≈0.023 M EUR, Cmat(WSiC PFC)≈1.463 t×110 ≈0.161 M EUR, Cmat(FLiBe)≈nominal 0.45 M EUR (0.30–0.60), Cmat(RAFM back)≈0.608 t×7≈0.004 M EUR. Process and QA costs (order of magnitude). •RAFM structure (lamination+machining+welding+QA): 0.20–0.26 M EUR (nominal 0.22). •NEH cartridge (W–SiC PFC machining, assembly, FLiBe cleaning/loading, microchannels, NDT): 0.35–0.50 M EUR (nominal 0.42). 40 Laser drivers, sensors, and auxiliaries (series). •Lasers + optics/fiber + windows/shutters + sensors: 0.80–1.00 M EUR (nominal 0.90). •Auxiliaries (piping/manifolds/valves/supports/insulation): 0.20–0.35 M EUR (nominal 0.28). Block Nominal mass Nominal cost (M EUR/cell) RAFM structure (lamination+mach.+weld.) 3.0–3.6 t Mat. ∼0.023; Proc. ∼0.22 ⇒0.24 W–SiC PFC (45 mm) 1.46 t 0.161 FLiBe breeder (120 mm) 0.62 t 0.45 RAFM back plate (30 mm) 0.61 t 0.004 NEH: materials (subtotal) ∼2.69 t 0.615 NEH: processes & QA –0.42 Lasers + sensors ≪0.1t0.90 Auxiliaries (fluid/supports) 0.2–0.3 t 0.28 Totals per cell ∼6.4–7.0t2.50 M EUR Table 8: Bottom–up breakdown of mass and cost per cell with RAFM structure and backplate, W–SiC PFC, and FLiBe breeder (baseline MVP). Typical ranges: 2.35–2.95 M EUR/cell depending on supplier and volume. Summary (MVP) and reinforcement options Cell (MVP): mcell ≈6.7t; Ccell ≈2.50 M EUR (range 2.35–2.95). Optional structural reinforcement: if verification of centrifugal/shock loads indicates low margins, add compression rings at the base edge, radial stays, and longitudinal stringers in RAFM. Typical impact: +0.2–0.5 t and +0.05–0.12 M EUR per cell, maintaining compatibility with docking and IGBI. Material sensitivity (per cell): •Solid W instead of W–SiC: +0.15–0.30 M EUR, +0.7–0.9 t. •LiPb instead of FLiBe: mbr →4.7 t; Cmat similar or lower, but +4 t of total mass (penalizes inertia). •Ti structure (SPF/DB+WAAM) instead of RAFM: −1.5–2.0t, but +0.25–0.45 M EUR/cell (processes and raw material). Technical notes. (1) RAFM baseline reduces CAPEX compared to Ti and improves lateral thermal spread relative to a Ti backplate. (2) FLiBe baseline minimizes the mass of fuel salt in the dome base; the 6Li enrichment surcharge is included in the range. (3) Structural reinforcements (rings, stays, stringers) are modeled as add-on kits per cell based on rotor dynamics and thermal shock results, without altering interfaces with service stations or IGBI. 4.13 Cost per rotor and per campus Assumptions. •Baseline cost per cell (RAFM + W–SiC + FLiBe): 2.50 M€. •Optional structural reinforcement (rings, stays, stringers): +0.05–0.12 M€/cell (nominal +0.08). •Net power per cell (calibration Secs. 4.1–4.3): Pe,cell = 2.03 MW. 41 6.3 Scenario B: Equivalence in land use (100 ha footprint) If 48 rotors ⇒25 ha, then 100 ha allow for 192 rotors: P192 = 192 ×121.8=23.386 GW, E192 = 192 ×1,013.6 = 194.62 TWh/year. Revenues at 75.9€/MWh: I192 ≈194.62 ×106×75.9≈14.77 B€/year. 6.4 Direct comparison Parameter Ref. fission (1.2 GW) MRFEP A (11 rotors) MRFEP B (192 rotors) Net capacity (MW) ∼1,200 1,339.8 23,385.6 Annual production (GWh) 10,512 (100% CF) 11,149.8 194,615 Estimated footprint (ha) 70–100 ∼5.7∼100 Commissioning 8–12 years 12–18 months (first rotor) progressive ramp-up Revenues at 75.9 €/MWh – ∼0.846 B€/year ∼14.77 B€/year High-level waste Yes No No Table 13: Comparison between a reference fission plant and MRFEP scenarios: A (energy equivalence) and B (land equivalence). Discussion. •With 11 MRFEP rotors, annual energy matches (and exceeds) that of a 1.2 GW nuclear plant, occupying only ∼6 ha, with monetization starting from the first rotor. •With equal footprint (100 ha), the MRFEP campus scales to ∼23.4 GW and ∼195 TWh/year, without high-level spent fuel. •The granularity (by rotor/cell) reduces financial and technical risk compared to monolithic projects with ≥8 years time-to-revenue. 6.5 Sensitivity notes •Electricity price: at 70−80 €/MWh revenues vary by ±6.5% approx. (linear with energy). •Availability:±1pp in ηavail ⇒ ±10.14 GWh/year per rotor and ±0.77 M€/year in revenues at 75.9 €/MWh. •Thermal efficiency: +10–20 K on the hot side (RAFM) contribute ∼0.5−1.5pp to Brayton (Sec. 5). 48 7 Future Work and Roadmap The present study outlines the conceptual feasibility of the Modular Rotating Fusion Engine (MRFE). Several aspects require dedicated modeling and experimental validation: •Coupled thermo–mechanical finite–element analysis of rotor–cell assemblies to validate clearance control under cyclic heating. •Detailed rotor–dynamic analysis including impulse asymmetries, bearing stiffness, and active magnetic bearing compensation bandwidth. •Monte Carlo neutronic simulations (MCNP, Serpent) quantifying neutron streaming through ports and confirming TBR margins. •Expanded economic sensitivity studies for first–of–a–kind plants, including BOP and civil works factors up to +70%. •Experimental validation of segmented sacrificial optics and hot–swap shutters under repeated neutron/gamma flux. These lines of research define the roadmap for consolidating MRFE as a viable path toward modular, continuous–operation fusion energy. 49 A Complementary and optional technologies This appendix compiles advanced technologies which, while not part of the reference design (baseline RAFM + W–SiC + FLiBe + Brayton cycle), may be considered as future optimization and extension pathways for the modular MRFEP system. A.1 Magnetohydrodynamic (MHD) conversion The use of a conductive liquid breeder (e.g. LiPb) opens the possibility of extracting additional power via direct MHD conversion in integrated ducts. This scheme exploits the Lorentz force on free charges in a flow transverse to a strong magnetic field (B= 5–10 T) generated by superconducting coils in the rotor hub. Physical model. j=σ(E+v×B),Eind =vB a, where σis the conductivity of LiPb, vthe flow velocity, and athe electrode spacing. The extractable power density is: p=σB2v2K (1+K)2, pmax =1 4σB2v2(K= 1). Design example. •Rectangular duct: a= 30 mm, h= 150 mm, L= 1.0m. •Flow: v= 3 m/s, σ= 106S/m, B= 5 T. •Net power: ∼0.14 MW/duct (with efficiency ηelec ∼0.6). Scaling. With two ducts per cartridge and 60 cartridges per rotor: PMHD,rotor ≈15–18 MW, providing 10–15% additional output, with ohmic heat returned to the Brayton cycle. The technology presents material challenges (electrodes, corrosion) and is considered optional, not included in the baseline economics. A.2 Direct conversion of radiation and particles Another exploratory pathway is direct capture of energy from charged particles and high-energy radiation: •Electrostatics for alphas: high-voltage grids to convert αkinetic energy into electricity. •Thermionic/photovoltaic cells: partial conversion of thermal radiation and bremsstrahlung. •Gamma radiation capture: still at a very preliminary stage, with low yields. These options are of academic interest but are not included in the baseline energy balance. 50 A.3 Advanced materials and hybrid breeders Alternative configurations to the FLiBe baseline can be considered: •Liquid LiPb: high performance for tritium breeding, but penalization in mass and higher corrosivity. •Be/SiC: as a neutron multiplier, compatible with RAFM. •MHD-compatible coatings: TiN, SiC, Al2O3to reduce parasitic currents in conductive flows. These options are classified as exploratory and for selective application. A.4 Other future optimization routes •HTS superconductors: more compact field coils with reduced cryogenic demand. •Integrated power electronics: MPPT and DC/AC conversion in each cartridge, for greater flexibility of grid coupling. •High-repetition optics: deformable mirrors and ultrafast OPCPA for operation in regimes >0.5 Hz. Taken together, these complementary technologies represent possible evolutionary extensions of the MRFEP. The present study focuses on the baseline architecture validated in cost and performance, leaving these pathways as a field for future research and development. 51 B Example of a Full-Scale MRFEP Plant Implementation This section describes a reference full-scale plant design for a Modular Rotary Fusion Energy Plant (MRFEP) based on a single rotor stack with N= 60 hexagonal pyramidal cells arranged in three axial tiers (20 cells per tier). The values presented are of order of magnitude, indicative and subject to civil/MEP refinement, and serve as a framework for comparison with fission plants in Sec. 6. B.1 Site layout and land requirements General plot. A plant with Pel,net ≃26–50 MW (Brayton+MHD) can be deployed on a fenced plot of ∼1–1.5 ha (12,000–15,000 m2), including main buildings, service yards, air-coolers or dry coolers, and a compact substation (132–220 kV). The footprint of the main power block is ∼0.3–0.5 ha. Zoning. The site is divided into: 1. Reactor Building (RB): houses the rotor stack and biological shielding. 2. Power Conversion Building (PCB): Brayton sCO2turbomachinery, heat exchangers and MHD converters. 3. Auxiliaries: vacuum, cryogenics, tritium handling, water treatment. 4. Administration and Control Building (A&C): control room, offices, QA/QC, HSE. 5. Electrical substation: grid connection, transformers and MCC. B.2 Reactor Building (RB): geometry and shielding Stack envelope. Each tier houses 20 cells with inner diameter Dfloor ≈19–20 m and clear height Hfloor ≈6m (ignition, coupling, cooling, inspection bay). The complete three-tier stack requires Hstack ≈ 18 m. Biological shielding. The RB integrates an inner lining of Ti-6Al-4V (50–80 mm), structural steel ribs, and a heavy concrete wall (barite/steel) of Tbio ≈1.5–2.0 m. The radius develops from the center: Rcells ∼9.5m, service ring (1–1.5 m) and shielding (1.5–2.0 m), yielding DRB ∼24–26 m and internal height ∼30 m. The external cylinder with lining and seismic clearance reaches 28–30 m in diameter and 32–35 m in height. Coupling arc and robotics. Each tier integrates a coupling arc with two robotic stations (Nxextraction, Nx+1 insertion). Corridors of 2.5–3.0 m and rails for robots are provided. On the roof, a 20–30 t overhead crane is installed for cartridges and larger components. 52 B.3 Underground reactor hall and shielded basements Concept. The stack is installed in a circular heavy reinforced-concrete underground pit, lined internally with metal, reducing surface volume and radiological “skyshine” risk. Geometry. Clear inner diameter Dpit ≈24–26 m, depth Hpit ≈18–20 m (3 levels of ∼6 m). Metal liner 50–80 mm, heavy concrete wall 1.5–2.0 m, and a peripheral gallery 1.5–2.0 m for services and robotics. Construction aspects. Includes waterproofing and drainage (sumps N+1), anti-buoyancy ballast or anchoring, double barriers at penetrations, nuclear-grade seismic reinforcement, and ventilation with chimneys and HEPA/catalytic filters for tritium management. Operation. NEH cartridges are exchanged from the top platform using robotic manipulators and the overhead crane. The underground configuration minimizes visible footprint and improves radiological containment. B.4 Power conversion and auxiliaries Brayton sCO2train. For Pth ≃30–72 MW, a Brayton cycle delivers Pel ≃11–32 MW (35–45% net). The PCB houses one or two CTG trains of 30–40 MW, with hot-side exchangers and recuperators. A hall of ∼40–50 m ×18 m is sufficient. MHD rectification. Two LiPb ducts per cell (Sec. ??) feed DC busbars and static converters. ∼120– 180 m2is allocated for busbars and DC cabinets per plant. Heat rejection. Air-coolers/dry coolers of 1,200–2,500 m2, with zero or minimal water consumption. Auxiliary services. A hall of ∼20m×12 m for vacuum, cryogenics, He/N2plant, and tritium extraction (double containment, double-wall piping). B.5 Personnel and Operations Shifts. 24/7 operation with three shifts: •Control room: 3–4 operators. •RB/PCB field technicians: 8–10. •Radiological/tritium protection: 2. •Utilities/security: 2–3. Total per shift: 15–20. Total staff: 60–90. B.6 Surface area and staffing comparison An MRFEP of 26–50 MW occupies 1–1.5 ha and requires 60–90 personnel. As a reference: a 600 MW fission unit occupies dozens of hectares and hundreds of staff; a 300–600 MW CCGT plant occupies 1–5 ha and 30–60 staff but uses fossil fuel. 53 Scenario Pel,net (MW) GWh/day Households (10,328 kWh/d) Conservative 26 0.624 ∼60,400 Nominal 38 0.912 ∼88,300 Optimistic 50 1.200 ∼116,200 Table 14: Daily energy and equivalent households supplied by an MRFEP (single rotor stack). B.7 Energy scenarios and household equivalents Full-scale implementation summary. 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